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991.
Two approaches to the strigolactone tricyclic lactone skeleton 2 were investigated using ketene/ketene-iminium cycloaddition to olefins. Finally, the first enantioselective access to the four stereoisomers of 5-deoxystrigol 1 is reported using an intramolecular [2+2] cycloaddition of homochiral ketene-iminium salts 5. Very high asymmetric control was achieved with C-2 symmetric pyrrolidines as chiral auxiliary. 相似文献
992.
A simple, convenient and efficient protocol for the construction of an array of glycospiro-pyrroloisoquinolines using isoquinolinium ylide and a carbohydrate-derived exocyclic olefin in the presence of Cu(OTf)2–Et3N catalytic system is described. Isoquinoline and alkylbromoacetates/2-bromoacetophenones were employed to generate the azomethine ylides in the presence of Et3N in refluxing toluene and subsequent exposure to the olefin led to the desired isoquinoline derivatives. 相似文献
993.
A simple method for the preparation of enantiopure furo[2,3-b]pyrroles, a rare class of concave bicyclic nitrogen and oxygen heterocycle, in promising yield has been developed. The 3-substituted pyrrolidinediones prepared from (2S,3S)-tetrahydro-3-hydroxy-5-oxo-2,3-furandicarboxylic acid (Garcinia acid) have been cyclized diastereo as well as enantioselectively to furo[2,3-b]pyrroles. The cyclization follows Baldwin’s rule. 相似文献
994.
Narsimha Reddy Penthala Nikhil Reddy MadadiVenumadhav Janganati Peter A. Crooks 《Tetrahedron letters》2014
Use of a novel reagent has been established for the synthesis of a series of 4,5-diaryl-2H-1,2,3-triazoles (6a–i and 9a–e) from cyanostilbene analogs of benzo[b]thiophene, benzo[b]furan, and indole, catalyzed by l-proline via Lewis base-catalyzed one-step [3+2]cycloaddition of azide. This method provides an efficient, simple, and environmentally benign procedure that affords good yields and relatively short reaction times. 相似文献
995.
Mehdi Adib Ehsan Sheikhi Pouyan Haghshenas Saideh Rajai-Daryasarei Hamid Reza Bijanzadeh Long-Guan Zhu 《Tetrahedron letters》2014
A novel one-pot, five-component synthesis of 1-(alkylimino)-5,5-dicyano-3a-aryloctahydro-3-oxacyclobuta[cd]pentalene-1a,2,5a,5b(2H,3aH)-tetracarboxylates is described. A mixture of phenacyl bromide, malononitrile, isocyanide, and two equivalents of a dialkyl acetylenedicarboxylate undergoes a novel 1:1:1:2 addition reaction at ambient temperature in absolute ethanol to produce diastereoselectively the title compounds in good yields. 相似文献
996.
Piyasena Hewawasam Yong TuThomas W. Hudyma Xiaofan ZhangRobert G. Gentles John F. KadowNicholas A. Meanwell 《Tetrahedron letters》2014
A convenient and practical synthesis of 6-carboalkoxy-13-cycloalkyl-5H-indolo[2,1-a][2]benzazepine-10-carboxylic acid derivatives (6) has been developed. The key step in the synthesis utilizes an intramolecular tandem reaction sequence of a Michael addition followed by a Horner–Wadsworth–Emmons (HWE) olefination reaction between hemi-aminal 11 and methyl 2-(dimethoxyphosphoryl)acrylate 12. The ring construction occurred efficiently and purification of the products 6 was straightforward. The C-10 methyl ester of 6a was hydrolyzed selectively to the carboxylic acid 13 while the olefin of 6d was converted to the cyclopropane 14 using trimethylsulfoxonium iodide in DMSO in the presence of NaH. 相似文献
997.
Pyrimido[4,5-d]pyrimidine derivatives 4 have been prepared in an efficient and regioselective manner in water via multi-component reaction of isothiocyanate 1, aromatic aldehyde 2, N,N-dimethyl-6-amino uracil 3 in the presence of p-toluenesulfonic acid (p-TSA) as a Lewis acid catalyst. 相似文献
998.
《Tetrahedron letters》2014,55(51):7094-7098
A new thiacalix[4]arene based fluorescent chemosensor thiacalix[4]arene-N-(quinolin-8-yl)acetamide (TCAN8QA) has been synthesized. TCAN8QA has been found to exhibit highly selective behavior for F− ions among all other anions, that is, Cl−, Br−, I−, PO4−3, OH−, H2PO4−, and CH3COO− in the absorption spectra as well as in the emission spectra. Red shift and quenching in emission spectra constituting the signature for fluoride detection are due to photoinduced charge transfer (PCT) which can be attributed to deprotonation of acidic NH proton in the presence of fluoride ions. 相似文献
999.
Ghasem Marandi Lotfali Saghatforoush Rafael Mendoza-Meroño Santiago García-Granda 《Tetrahedron letters》2014
The synthesis of a number of 3-(alkylamino)-2-arylimidazo[1,2-a]pyridine-8-carboxylic acids via a facile route involving the reaction between 2-amino-3-pyridinecarboxylic acid, benzaldehyde derivatives, and isonitriles is reported. The structures of the synthesized compounds are proved by X-ray crystallography. 相似文献
1000.
Guang‐Ming Liang Jing Shang Kun‐Guo Yang Kai Ma Qing‐Ling Ni 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(4):379-383
The title compounds, bis{μ‐N‐[(diphenylphosphanyl)methyl]pyridin‐4‐amine‐κ2N1:P}disilver bis(perchlorate) acetonitrile monosolvate, [Ag2(C18H17N2P)2](ClO4)2·CH3CN, (1), and bis{μ‐N‐[(diphenylphosphanyl)methyl]pyridin‐4‐amine‐κ2N1:P}bis[(nitrato‐κ2O,O)silver], [Ag2(C18H17N2P)2(NO3)2], (2), each contain disilver macrocyclic [Ag2(C18H17N2P)2]2+ cations lying about inversion centres. The cations are constructed by two N‐[(diphenylphosphanyl)methyl]pyridin‐4‐amine (DPP) ligands linking two Ag+ cations in a head‐to‐tail fashion. In (1), the unique Ag+ cation has a near‐linear coordination geometry consisting of one pyridine N atom and one P atom from two different DPP ligands. Two ClO4− anions doubly bridge two metallomacrocycles through Ag...O and N—H...O weak interactions to form a chain extending in the c direction. The half‐occupancy acetonitrile molecule lies with its methyl C atom on a twofold axis and makes a weak N...Ag contact. In (2), there are two independent [Ag(C18H17N2P)]+ cations. The nitrate anions weakly chelate to each Ag+ cation, leading to each Ag+ cation having a distorted tetrahedral coordination geometry consisting of one pyridine N atom and one P atom from two different DPP ligands, and two chelating nitrate O atoms. Each dinuclear [Ag2(C18H17N2P)2(NO3)2] molecule acts as a four‐node to bridge four adjacent equivalent molecules through N—H...O interactions, forming a two‐dimensional sheet parallel to the bc plane. Each sheet contains dinuclear molecules involving just Ag1 or Ag2 and these two types of sheet are stacked in an alternating fashion. The sheets containing Ag1 all lie near x = , , etc, while those containing Ag2 all lie near x = 0, 1, 2 etc. Thus, the two independent sheets are arranged in an alternating sequence at x = 0, , 1, etc. These two different supramolecular structures result from the different geometric conformations of the templating anions which direct the self‐assembly of the cations and anions. 相似文献